Abnormal proliferation or apoptotic pathways disrupt homeostasis of the colonic mucosa, modulating risk for, and progression of, colon cancer. However, defects in the cellular mechanism(s) that integrate these pathways may have more profound affects on homeostasis and the tumorigenicity of a cell than defects in either individual pathway. We have previously established that butyrate, a natural constituent of the colonic contents, is a potent mediator of growth arrest and apoptosis in SW620 human colonic carcinoma cells. We also found that an intact deltapsimu (mitochondrial membrane potential) is required for the induction of apoptosis and, to our surprise, the initiation of growth arrest as well. Thus, we have hypothesized that the deltapsimu plays a critical role in integrating the signals that link cell cycle arrest and apoptotic cascades and, therefore, in determining the tumorigenic potential of a cell. To test this hypothesis, we have generated novel isogenic clones of SW620 cells that exhibit stable, significant alterations in basal deltapsimu. Consistent with a role in integrating proliferation and apoptosis, and in determining tumorigenicity, we found that the basal deltapsimu is significantly linked to the sensitivity of these cells to butyrate, and their ability to grow under adhesion-compromised conditions (preliminary data). Utilizing these unique cells, Aim 1 of this application dissects the impact of basal deltapsimu on butyrate sensitivity by defining the link between deltapsimu and the activity, subcellular distribution and interactions of p21WAF1/Cip1, TR3 and Smac, each of which have been implicated in integrating cell cycle arrest and apoptotic cascades. Aim 2 defines the impact of basal deltapsimu on the intracellular distribution of mitochondria and determines the relationship between deltapsimu- linked altered sensitivity to butyrate and mitochondrial distribution. Aim 3 dissects the affect of basal deltapsimu on tumorigenicity in vivo, and also recapitulates the deltapsim- linked altered sensitivity to butyrate by growing cells as xenografts in nude mice maintained on control or tributyrin diets. Finally, aim 4 couples our isogenic cell lines, the microarray facilities at Albert Einstein College of Medicine and the expertise of members of our group, to generate databases that profile the ground state of altered basal deltapsimu and the linked altered sensitivity to butyrate. These databases are integrated with those established by our group that profile numerous colonic epithelial cell maturation pathways to define the role of deltapsimu in maturation and provide critical insight into the molecular mechanisms associated with colon cancer risk and progression.